A percussive shearing drill bit is known and described in U.S. Pat. No. 6,253,864. FIG. 4 of said US patent depicts a percussive shearing bit having a unitary body, a means for attachment to a drill string, and a plurality of blades housing a plurality of shear cutting elements. Fluid outlets are situated on the head of the unitary body between the blades. The blades consist of a series of receptacles to house the shear cutting elements and a shelf that runs along each blade before the cutting elements. The shelf serves to direct cuttings away from the operative surface of the bit.
In operation, the known percussive shearing drill bit is rotated about its longitudinal axis shearing off the rock formation as the drill bit rotates. A hammer simultaneously impacts the bit thereby providing an additional percussive drilling force. The shear cutting elements have been specially designed to withstand the unusual stresses induced by combined percussive/shear drilling, in that a distal portion of the shear cutter has been rounded to prevent large localised stresses in the cutters.
It is thus a disadvantage of this known percussive shearing drill bit that its requires commodity shear cutting elements. In these commodity shear cutting elements a compromise is found for both shearing and axial cutting. Since the compromise is based on the rounded shape of the distal portion, the compromise is lost upon wear of the shear cutting elements which forms another disadvantage of this known percussive shearing drill bit.